We are interested in the regulation of gene expression in sea urchin embryogenesis. We have isolated two cDNA clones specifying mRNAs that are members of a small family of mRNAs. The mRNAs code for a group of approximately ten low molecular weight acidic proteins that accumulate in the embryonic ectoderm. The function of these proteins is unknown, but they are among the most actively synthesized proteins in later embryonic stages and undergo the most pronounced developmental changes observed during embryogenesis. The mRNAs accumulate in mass over 100 fold during embryogenesis and have a common repetitive element at their 3 foot ends. This element is present in thousands of sites in the sea urchin genome. In situ hybridization to sections of embryos suggest that the RNAs are present in a specific cell type. They appear in the dorsal ectoderm of the pluteus larva and in the future dorsal ectoderm of the gastrula stage embryo. We propose further in situ experiments to map this cell lineage to earlier developmental stages. Using recombinant DNA methodology, we plan to establish the number, arrangement, and structure of the genes coding for the ectoderm proteins. By preparing antibodies to two or three of the more abundant ectoderm proteins, we propose experiments to determine the location and possible function of these proteins in the embryo. Our ultimate objective is the isolation and characterization of embryonic regulatory elements involved in the expression of these genes. Using lysates of embryos at appropriate developmental stages, we will attempt to achieve accurate and specific in vitro transcription using the cloned ectoderm genes and their upstream sequences as templates.